The present invention relates to an apparatus for handling pipe fitting, tools, and other apparatus located on the marine floor. In particular the present invention relates to a crane for holding and manipulating pipe.
Enormous expense and effort are given to extraction of oil from submerged lands, and much new apparatus and technique is arising therefrom. Large pipelines are laid on the marine floor by elaborate, costly vessels which form continuous pipe and feed it over the stern, using highly developed technique. The prior art does not offer fully satisfactory methods or apparatus to connect such pipe at its end after it is laid.
The pipe being laid is of very large proportions for example 36 to 48 inch diameter. Hence, the problems are of equal proportion. Since current exploration and oil development are going on in the most hostile environments which exist on the face of the earth, it is not infrequent that the laying of the pipeline must be terminated and the pipe cut loose and dropped from the vessel in order for the vessel to move out of the way of a storm, for example in the North Sea or one of the areas off Alaska coast such as Cook Inlet. These interruptions as well as the completion of the laying operation and the joining of the laid pipe to either another pipe or to some other connection means that these problems of handling the end of the pipe under the marine surface, at the marine floor, occur frequently.
When a pipeline laying has been completed or interrupted, its loose unconnected end lies on the marine floor, probably out of line with and a few feet from a fitting, perhaps on another pipe, or coupling point. The mating ends are misaligned and separated, perhaps by several degrees and several feet, (up to a few hundred feet) and the ends may be partly buried in the soil. In the prior art, two approaches have been used to align the pipe and make the connection. There is the cheap, dangerous approach of sending a diver down, then wrestling the pipe around by means of shipboard cranes with lines extending to the pipe and then hoping that the diver can, using traditional tools for dry land work, make the connection. The movement of the ship makes this difficult and dangerous.
Then there is the incredibly expensive approach of using a unitary diving manipulator, having air locks and pipe handling claws and bending devices, elaborate controls, and highly automated coupling devices. The present invention overcomes many of the disadvantages in the prior art, by providing apparatus intermediate in cost but superior in capability.
Just as there are two handling apparatus schemes in the prior art, so are there two fitting schemes. The first and simpler method is to move the pipe, by some means, to an approximately aligned position, measure and guage the opening, then to fabricate a spool piece or other fitting on the deck of an attending vessel. This method has the disadvantage of requiring accurate measurement and of requiring that the laid pipe not be moved after guaging. It is sometimes difficult to insert the spool piece, which had to be precisely made, without causing motion of the pipe ends, thereby misaligning them, or damaging them or without dragging dirt into the coupling.
This method is probably the best since it is the simplest. Very frequently simple flange connections are employed. The more expensive and elaborate fitting schemes all provide for adjustable and costly and often unreliable couplings, perhaps including ball joints, telescoping fittings, or biascut revolving flanges. Each of these fittings seems reasonable for applications, but the present invention provides improvement, either for installation of fixed or adjustable fittings.
The elaborate adjustable couplings have been widely accepted and used in the art, for two principle reasons. The first reason is that almost no suitable means existed when the sudden almost explosive exploration in the North Sea began. And a second consideration was the prospect that the expensive adjustable fittings formed absolutely tight seals, wherein there would be no leak and the seals would create a joint stronger than the original pipe. It has been found that there are leaks, which are of a small extent and probably at the present rate are of no environmental consequence. However, the exploration companies are no longer satisfied with paying enornous amounts of money for devices which function possibly not as well as simpler devices. Furthermore, now that there has been a period of study and appreciation of the problem, a more careful and logical approach to the engineering aspects of undersea operations has been possible with the result that among others that the present invention has occurred.
In background, the reader should consider the difference between cranes for use on land and those for use under water in pipeline work. A crane for use in air must be able to lift loads vertically, but is not required to exert lateral pressure. Underwater cranes must resist currents, which will exert large forces on large objects. A crane ashore usually is mobile; a crane on the marine floor need not be, since it is attended by vessels, all of which themselves have cranes which can place the crane on the marine floor near its work. A crane in air may have exposed mechanism; a submerged crane must have simple, corrosion resistant bearings and mechanisms, or must be housed in costly ways.
Because of the lateral current force problem, buoyant devices such as balloons, are not useful when used alone. There must be lateral restraints and lateral motive means.
A feature of the invention is to provide method and apparatus for coupling pipes and installing devices by crane means on the marine floor, with improved costs, safety, and reliability. Particular advantages include provision of improved means:
(1) to align two ends of submarine pipeline for coupling
(2) to manipulate and adjust pipe fittings
(3) to lift damaged pipe for repair
(4) to provide tool handing means to a diver
(5) to provide for remote and precise control of coupling processes
(6) to provide means for handling pipes and any other equipment which may be attached to pipe or used while working on a pipeline.